Hi Tanja,
Thank you for sharing information and screenshots.
Since the issue appears to be related to how the gaming installation services are detecting available drives, I would suggest first checking whether the Xbox app shows the same behavior. Open the Xbox app, select your profile picture in the top-right corner, then go to Settings > Install Options. Under Installation Drive, try selecting the D: drive and save the change. Because the Xbox app and Microsoft Store share the same game installation settings, this can help determine whether the issue is isolated to the Store interface or affects the underlying game installation service as well.
If D: still cannot be selected, try repairing both the Microsoft Store and Xbox app. Open Settings > Apps > Installed apps, locate each app, select the three dots menu, choose Advanced options then click Repair. If the issue persists, return to the same page and select Reset. Once complete, restart the PC and test the installation again.
You could also try temporarily changing the default app save location. Navigate to Settings > System > Storage > Advanced storage settings > Where new content is saved, change New apps will save to from D: to C:, select Apply, restart the PC, then switch the setting back to D: and restart once more. This can help refresh the storage location settings used by Microsoft Store apps.
I hope this helps. Please let me know the results of these tests and I'll be happy to continue investigating further.
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